In an example of an angular indexing apparatus for a machine tool, the following simultaneous 5-axis control machining apparatus is known. The machining apparatus is a parallel supporting type in which a rotating drive motor that indexes an angle is built in a head supporting section, the lower portion of a vertical head is connected to the lower portion of an oblique drive shaft that is rotated by the rotating drive motor, and a vertical tool main shaft is rotatably supported in the head. In addition, the rotating drive motor is one including a rotor and a stator, that is, what is called a DD motor (direct drive motor) is singly used (one DD motor is used) for it. (Patent Document 1)
In a different example of an angular indexing apparatus for a machine tool, there is known one in which a shaft, to whose one end an indexing table is mounted as a rotating indexing table, is rotatably supported in a casing and in which a DD motor is accommodated between the casing and the shaft. (Patent Document 2)
Although not discussed in the aforementioned patent documents, in general, a cable that is wired towards the outside of the apparatus is connected to the DD motor. Examples of the cable are a current supply cable for supplying current to a stator coil; a ground wire; and a detection wire for detecting abnormality of the drive motor. In addition, wiring methods of the cable generally include a first method in which the cable is passed through a space between the drive shaft and a housing (head supporting section, casing) that accommodates the DD motor, and a second method in which the cable is drawn out to an outer peripheral side of the housing from near a portion where the DD motor and the cable are connected to each other.
However, in the first method, when a component is provided between the housing and the drive shaft, there is no space for passing the cable, thereby forcing one to use the second method.
In the second method, when the cable in an exposed state is wired, the cable may become damaged. In particular, when the cable is exposed and wired near a portion where mounting and removal are performed with respect to a machine tool, the probability of the cable becoming damaged when performing the mounting and the removal with respect to the machine tool is high. In addition, since the cable is drawn out from near a portion where the DD motor and the cable are connected to each other, almost all of the cable is exposed, as a result of which the probability of the cable becoming damaged is high.
Accordingly, when the second method is used, if a protective cover for the cable is attached to the outer side of the housing, the outside diameter of the housing is correspondingly increased in size, which is not desirable. This is because, when the angular indexing apparatus is mounted to a predetermined mounting position of the existing machine tool, if the outside diameter of the housing is increased from a present outside diameter, the angular indexing apparatus cannot be mounted as it is to the existing machine tool, thereby making it necessary to modify the machine tool itself.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2-116437 (page 9, lower column; FIG. 16)
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 4-289042 (claims, FIG. 4)